In packaging non-carbonated juices and other similar products, it is desirable to pack and seal them in their heated and sterile condition in a sterile container. When the non-carbonated juice and head space gases cool to ambient temperature in the sealed container, the juice and gases decrease in volume. This decrease in volume causes a drop in pressure within the container. The container must be either structurally strong enough to withstand this pressure drop without being affected, or must in some way positively respond to the pressure drop or the container walls will collapse in places, which is undesirable.
A form of container that is desirable for use as a hot-fill container is a convolute container. These containers are inexpensive to manufacture compared to metal cans, but their walls would collapse to some degree if subjected to the vacuum pressure created within the container as the hot-fill material and internal gases cool to ambient temperature and the end closure structures of the container are substantially nonflexible.
The prior art discloses structures that positively respond to a reduction in pressure in a container caused by cooling of the contents in the container after sealing. Japanese Publication No. 58-99391; Japanese Publication No. 57-202911; and Japanese Publication No. 58-216586, all disclose apparatus that positively respond to a reduction in volume and a resulting decrease pressure in the container by reducing the cross-sectional area of the container as the hot-fill material and gases within the container cool to ambient temperature. Each reference discloses the use of fold or score lines in the side walls to allow them to uniformly fold inwardly to reduce the cross-sectional area of the container. U.S. Pat. Nos. 2,293,142 and 2,340,473 disclose apparatus with a body that can expand and contract in response to the changes in the volume of the contents of material packed in the container, and pressure within the container. These references also disclose the use of fold or score lines for providing a uniform reduction in cross-sectional area in response to the volume and pressure changes within the container.
In the prior art, end closure structures have also been used to positively respond to changes in the volume of the contents of material packed in the container and/or pressure within a container. In U.S. Pat. No. 3,057,537, the lid for a paper cup is adapted to move outwardly in response to hot gases from hot coffee or other hot liquids in a container. However, this lid is not designed to move inwardly from its original static position. In U.S. Pat. No. 3,135,451, the lid of a container is drawn to a concave shape by the vacuum pressure in the container. However, this lid is a heavy gauge lid, not particularly flexible, and does not have a thin closure member covering an opening in the lid. In U.S. Pat. Nos. 2,894,844 and 2,379,043, relatively heavy gauge lids and bottom closures disposed on structurally strong containers are initially concave and caused to be pushed outwardly to a convex shape by gases developed by the contents of the container over time. These end closures structures are of this heavy gauge to withstand the internal pressures of the container.
Besides the top end closure structures being adapted to positvely respond to volume and/or pressure changes in the container, the prior art discloses a bottom closure structure for the same purpose. The Article entitled, "Introduction of a New Paperboard Container Filling System for Non-Carbonated Drinks", Packaging Japan, Vol. 4, No. 18, November, 1983, discloses a laminate paperboard can with a rigid top closure structure and deformable bottom closure structure. The bottom closure structure is inwardly deformable to response to changes in the internal pressure of the container. However, the can is designed for vacuum packing products. By vacuum packing the contents there is significant stress of the seal associated with the opening in the top end closure structure and closure member covering the opening. Because of this stress, the seal is susceptible to becoming oxygen permeable over time.
The prior art also discloses safety-type openings for a can lid. However, as disclosed in U.S. Pat. Nos. 3,380,622 and 4,253,584, the safety openings have a rolled edge to prevent injury to the user, but they only allow for one seal between the lid and closure member covering the opening.
All of the above cited prior art references have inherent problems that would make them undesirable for use on a convolute hot-fill container. The present invention overcomes these problems, and provides an easy to manufacture, simple, inexpensive end closure structure for hot-fill containers to positively respond to a reduction in the volume in the material and gases in the container, and a resulting decrease in pressure in a hot-filled container.